Silver complex diffusion transfer process

ABSTRACT

IN A DIFFUSION TRANSFER COPYING PROCESS USING A UNITARY COPYING MATERIAL HAVING AN EXTERNAL SILVER HALIDE EMULSION LAYER AND AN IMAGE-RECEIVING LAYER ON A COMMON SUPPORT, REMOVAL OF THE EMULSION LAYER FROM THE DEVELOPED IMAGE LAYER BY SIMPLE WASHING A FACILITATED BY PROVIDING A NATURAL OR SYNTHETIC MACRO MOLECULAR CARBOHYDRATE COMPOUND HAVING A NUMBER OF PAIRS OF CIS-HYDROXYL GROUPS THEREON AS THE ESSENTIAL BINDING AGENT OF THE EMULSION LAYER OR OF A SUPPLEMENTAL LAYER INTERMEDIATE THE EMULSION LAYER AND IMAGE-RECEIVING LAYER, AND CARRYING OUT THE DIFFUSION TRANSFER TREATMENT OF THE MATERIAL AFTER IMAGEWISE EXPOSURE WITH AN AQUEOUS ALKALINE PROCESSING LIQUID IN THE PRESENCE OF BORATE ANIONS WHICH CROSS-LINK WITH THE MACRO MOLECULAR CARBOHYDRATE TO FORM A PH-REVERSIBLE GEL WHICH SI INSOLUBLE IN AN ALKALINE SOLUTION BUT BECOMES AT LEAST SUBSTANTIALLY SOLUBLE IN A NONALKALINE SOLUTION.

Patented Aug. 15, 1972 3,684,508 SHJVER COMPLEX DIFFUSION TRANSFER PROCESS Emiel Alexander Hofman, Mayerlei 218, and Camille Angelina Vandeputte, Molenler 100, both of Mortsel, Belgium No Drawing. Filed Feb. 28, 1969, Ser. No. 803,418 Claims priority, application Great Britain, Mar. 1, 1968, 10,197/68 Int. Cl. G03c 5/54 US. C]. 96-29 20 Claims ABSTRACT OF THE DISCLOSURE In a diffusion transfer copying process using a unitary copying material having an external silver halide emulsion layer and an image-receiving layer on a common support, removal of the emulsion layer from the developed image layer by simple washing is facilitated by providing a natural or synthetic macro molecular carbohydrate compound having a number of pairs of cis-hydroxyl groups thereon :as the essential binding agent of the emulsion layer or of a supplemental layer intermediate the emulsion layer and image-receiving layer, and carrying out the diflusion transfer treatment of the material after imagewise exposure with an aqueous alkaline processing liquid in the presence of borate anions which cross-link with the macro molecular carbohydrate to form a pH-reversible gel which is insoluble in an alkaline solution but becomes at least substantially soluble in a nonal'kaline solution.

The present invention relates to a method of producing photographic images according to the silver complex diffusion transfer process generally known in the art.

According to a specific embodiment of this process a so-called multilayer material is used comprising both the image-receiving layer and the light-sensitive silver halide emulsion layer applied to a same support sheet. The light-sensitive layer may be present on top of the imagereceiving layer and may be removed after the transfer image formation has taken place, e.g. by means of an auxiliary sheet brought in contact therewith or by means of a subsequent rinsing bath in which the silver halide emulsion layer dissolves or detaches in the form of small flakes or as a coherent membrane.

The methods known in the art always show one or more disadvantages. So, often unusual and less suitable binders have to be used in the preparation of one or more of the composite layers of the multilayer material. Further, for the removal of the emulsion layer often warm water having a temperature of about 35 to 50 C. has to be used. Another very important disadvantage frequently occurring is the fact that the silver halide emulsion layer easily tends to release already in the alkaline processing liquid, which results in the production of a diffusion transfer copy of an inferior quality and whereby the complete removal of the emulsion layer becomes more complicated.

The present invention provides a method according to which these disadvantages may be overcome by incorporating a macromolecular compound having available cishydroxy groups into the light-sensitive silver halide emulsion layer and/or into a layer situated between the emulsion layer and the underlying image-receiving layer of a multilayer material for producing images according to the silver complex diffusion transfer process, and by carrying out the diffusion transfer image formation with an alkaline processing liquid in the presence of orthoborate anions. The light-sensitive emulsion layer is then removed without mechanical help by means of an aqueous rinsing liquid.

Thus, the present invention relates to a method for the production of photographic images according to the silver complex diffusion transfer process using a multilayer material comprising in order a support, an image-receiving layer and a light-sensitive silver halide emulsion layer, the latter layer and/or a supplemental layer occasionally present between the emulsion layer and the image-receiving layer having incorporated a macromolecular compound having cis-hydroxy groups, wherein the imagewise exposed multilayer material is treated with an aqueous alkaline processing liquid in the presence of orthoborate anions and then after the diffusion transfer image has been produced, is treated with an aqueous rinsing liquid for removing the emulsion layer without substantial mechanical help.

Suitable macromolecular compounds having cis-hydroxy groups are water-soluble gum mucilages, e.g. gum arabic, some polysaccharides and derivatives thereof such as mannans and galactomannans, alginates, monoglyceryl esters of pectic acid and hydroxyalkyl starches or hydroxyalkyl celluloses, e.g. hydroxyethyland hydroxypropyl starch, and some synthetic substances such as partially saponified polyvinyl acetates and polyvinyl alcohol. The available cis-hydroxy groups preferably are present in l-2 position, but in some cases they may be present in another position, e.g. in 1-3 position, as is the case of many pairs of hydroxyl groups of partly or wholly saponified polyvinyl acetate. The macromolecular compound contains at least several pairs of cis-hydroxyl groups per macromolecular chain. Often two or more of such types of compounds are used together. The macromolecular compound for use in carrying out the method of the present invention preferably shows film-forming characteristics per se, in other words is a binder. However, this is not an essential requirement, and also nonfilm-forming macrcomolecular compounds may be used, which gel in situ at the preparation stage of the material or at the processing stage as detailedly described further in the description.

If no supplemental layer is present between the emulsion layer and the receiving layer, the former contains the macromolecular compound(s). This (These) com pouud(s) preferably constitute(s]1 about 10 to about 70% by weight on the total weight of the binder of the silver halide emulsion layer. Larger amounts generally impair the photographic characteristics of the emulsion layer and for that reason mostly are not applied. The macromolecular compound may be added to the light-sensitive coating composition at any stage of the preparation, e.g. before the precipitation of the light-sensitive silver halide, or just before coating.

At the application stage of the alkaline processing liquid for carrying out the development and the diffusion transfer image formation, the silver halide emulsion layer is strengthened in situ due to the gelification of the macromolecular compound by the orthoborate anions in an alkaline medium. Later on, in the aqueous rinsing liquid the strong gel structure loosens and the emulsion layer dissolves or detaches in the form of more or less small flakes.

In the manufacture of the multilayer material often at least one intermediate layer is applied between the imagereceiving layer and the light-sensitive silver halide emulsion layer. This intermediate layer performs a better contact between the receiving layer and the emulsion layer and is further intended to improve the adherence of the emulsion layer to the receiving layer before and during processing and to facilitate the separation of the emulsion layer after processing. However, in practice often the emulsion layer already detaches in the alkaline processing liquid, which results in image failure and contamination of the alkaline processing liquid.

Accordingly to the present invention this difiiculty may be completely avoided by incorporating a macromolecular compound having available cis-hydroxy groups into the silver halide emulsion layer as detailedly described above, and/or by incorporating a same type of compound into an intermediate layer between the receiving layer and the emulsion layer. In such an intermediate layer the macromolecular compound having cis-hydroxy groups preferably is present in an amount of at least by weight on the total weight of the binder. In many cases the said macromolecular compound forms the sole and total amount of binder in the intermediate layer. If it has 'no film-forming charcateristics per se, it may gel in situ at the preparation stage of the multilayer material, e.g. in an alkaline medium and by means of orthoborate ions present in the coating composition or diffusing from another layer of the multilayer material.

' At the stage of the application of the alkaline processing liquid the said macromolecular compound present in the intermediate layer is strengthened as described above and so ensures a good adhesion of the emulsion layer to the image-receiving layer; later on, at the rinsing stage with the aqueous rinsing liquid, the strong" gel structure of the macromolecular compound loosens and the intermediate layer dissolves. Hereby the emulsion layer detaches without mechanical help. Depending on the nature of the latter layer, it also dissolves, or detaches in the form of flakes or as a coherent membrane.

Suitable compounds providing the boration in an aqueous medium are the following water-soluble oxygenboron compoundszorthoboric acid and salts thereof, metaborates, polyborates such as tetraborates, e.g. borax and sodium tetraborate, and pentaborates, e.g. potassium pentaborate.

There are a number of ways in which the orthoborate ions may be supplied. The compound providing the boration may be incorporated into at least one layer of the multilayer material, e.g. into the image-receiving layer, into the light-sensitive silver halide emulsion layer and/ or into another layer occasionally present, e.g. an adhesive and separating layer applied between the image-receiving layer and the light-sensitive silver halide emulsion layer. If the material comprises a paper support it is also possible to incorporate into the said support a considerable amount of the compound providing the boration and even the whole of it. Preferably an amount of from about 100 mg. to about 50 g. of compound providing the boration is applied per sq.m. of the multilayer material.

The present invention also relates to a multilayer material for use in carrying out the method of the present invention, wherein a compound providing orthoborate anions is present in at least one layer of the multilayer material.

Instead of or in addition to incorporating this compound into the multilayer material, it is a preferred embodiment of the method of the present invention to add at least a part and preferably even the total-amount of this compound to the alkaline processing liquid for carrying out the diffusion transfer image formation. The compound(s) providing the orthoborate ions maybe added to this processing liquid in an amount preferably equivalent to from about 0.2 g. to about 20 g. of boric acid per litre of this solution. It is even possible to supply the compound(s) providing the orthoborate ions by means of a separate liquid (other than the alkaline processing liquid) with which the light-sensitive material is wetted after preparation and before the treatment with the alkaline processing liquid for carrying out the development of the silver halide emulsion layer and the formation of the diffusion transfer image.

In carrying out the method of the present invention the photographic multilayer material is image-wise exposed to an original. This exposuremay be done in a camera or other exposure unit generally known in the art.

Then the multilayer material is wetted with an alkaline processing liquid in order to develop the silver halide emulsion layer and to have unexposed silver halide complexed and diffused from the non-image areas of the silver halide emulsion layer onto and into the imagereceiving layer, where it will be converted so as to form a visible image.

Of course, this treating step is carried out in the presence of developing compounds, a complexing agent for silver halide and orthoborate ions. The aqueous alkaline medium of the processing liquid sets free the orthoborate ions from the compound producing boration. The orthoborate ions make set the macromolecular compound having cis-hydroxy groups and being present in the silver halide emulsion layer and/or 'inan underlying layer on top of the image-receiving layer, in that probably a threedimensional structure is formed. Hereby the strength of the layer is increased and also the adherence of the emulsion layer to the image-receiving layer is improved. In this way the risk of a premature loosening of the emulsion layer during the treatment with the alkaline processing liquid entailing all kinds of harmful effects is completely avoided. However, at the subsequent treating stage with a neutral or slightly acidic aqueous rinsing liquid, the three-dimensional structure of the macromolecular compound having cis-hydroxy groups with the borate ions is ruptured, whereby the silver halide emulsion layer dissolves or detaches as a coherent sheet or in the formof more or less small flakes. The aqueous rinsing liquid may comprise a minor amount of an oxidizing agent, e.g. a water-soluble periodate, in order to still further accelerate the destruction of the links between the macromolecular chains. In fact the macromolecular compound having cishydroxy groups gels due to the formation of borate links between the chains in an alkaline medium. However, the gel thus produced in situ is a reversible gel, in other Words it has a dynamic structure. This means, that in a neutral or slightly acidic aqueous medium the borate links are ruptured and a two-dimensional water-soluble form is produced again. Hereby an easy and complete removal of the emulsion layerv in the aqueous rinsing bath is effected.

The exposure step, the development step and the rinsing step of the multilayer material may be carried out in suitable apparatus generally known in the art. The three processing steps may be carried out in a compact and automatic processing unit comprising at least two and even all the treating stations for carrying out the method of the present invention. The photographic multilayer material may be supplied in sheet form or in roll form. After thelimage-wise exposure it is wetted with an aqueous alkaline processing liquid for carrying out the diffusion transfer image formation. This wetting may occur according to any technique known in the art, e.g. by dipping, spraying, spreading a viscous alkaline paste, by means of a licking roller, etc. Suitable alkaline substances are alkali hydroxides, alkali. carbonates, phosphates and borates. Particularly, the alkali borates are very suitable since they provide borate ions at the same time. The treatment of the multilayer material with the alkaline processing liquid occurs in the presence of the compounds necessary for carrying out the diffusion transfer image formation, viz. at least one developing compound, a complexing agent for silver halide and (a) substance(s) for converting the diffusing complexed silver halide into a visible image. The latter substance(s) is (are) provided in and/or on top of the image-receiving layer situated under the silver halide emulsion layer. They are generally called development nuclei and even shortly nuclei. Chemical as well as physical development nuclei, both generally known in the art, are suited for the purpose of the present invention. The complexing agent for the undeveloped silver halide is added preferably to the alkaline processing liquid. However, it may also be incorporated at least partially into the image-receiving layer or into another layer of the multilayer material other than the silver halide emulsion layer. The developing compound(s) may be added to the alkaline processing liquid, but according to a preferred embodiment at least part and even 'the whole amount of the developing compound(s) is incorporated into at least one layer of the multilayer material, whereby the processing liquid becomes a mere alkaline liquid that is substantially free from developing compound and that consequently shows better keeping qualities. A combination of hydroquinone and a 3-pyrazolidinone developing compound is preferably used. All types of development nuclei, complexing agents for silver halide and developing compounds generally known in the art of the silver complex diffusion transfer process are suited for use in carrying out the method of the present invention. These compounds may be applied in the usual concentrations so that further information is considered to be superfluous.

The final treatment of the multilayer material with an aqueous rinsing liquid for removing the light-sensitive emulsion layer may be carried out in Whatever way. The aqueous liquid may be sprayed onto the multilayer material, but preferably this material is conducted through the aqueous bath. It is not necessary to use warm water, water at room temperature and even at a lower temperature being suitable for carrying out this processing step. The rinsing liquid is neutral or preferably slightly acidic. The emulsion layer dissolves or detaches in flakes or as a whole depending on its nature as already explained above. A very complete and easy removal of the emulsion layer takes place.

The multilayer material for use in carrying out the method of the present invention in order comprises a suitable support, an image-receiving layer and a lightsensitive silver halide emulsion layer. According to a preferred embodiment an adhesive layer is present between the image-receiving layer and the emulsion layer as described above.

The support may be a paper support or a transparent hydrophobic synthetic film support such as a cellulose ester support, e.g. a cellulose triacetate support, or a polyester support, e.g. a biaxially stretched polyethylene terephthalate support.

The image-receiving layer preferably is a usual hydrophilic colloid layer, e.g. a gelatin layer, containing development nuclei in and/or on it. The image-receiving layer mostly is hardened e.g. with a common hardener such as formaldehyde or glyoxal or by means of a latent hardener which effects its hardening action only in an alkaline medium, in this case at the development stage. The latent hardener may be a hydrophilic colloid binder, e.g. the propylene glycol ester of alginic acid, which forms parts of the binder of the image-receiving layer. For more details hereon reference may be made to the United Kingdom patent specification 962,483 filed Jan. 1, 1962 by Agfa AG.

In order to improve the flexibility of the image receiving layer often a latex, e.g. a polyethyl acrylate latex, is incorporated therein, preferably in an amount between and 100 percent by Weight of the hydrophilic colloid binder of the image-receiving layer.

The capability of writing on the finally obtained copy can be considerably improved by incorporating a matting agent into the image-receiving layer. Finely divided inorganic pigment particles, e.g. particles of barium sulphate, china clay or silica, are especially suitable for this purpose. The pigment particles preferably are applied in an amount of between 0.5 and 3.0 g. per sqm: of the image-receiving layer.

The light-sensitive layer may be any silver halide emulsion layer provided its exposed silver salt, during the diffusion transfer process, is rapidly enough developed and its unexposed silver salt is rapidly enough complexed.

The silver halide emulsion layer may be highly sensitive in order that exposures can be made therewith in a camera. The emulsion layer may be low sensitive if it is to be exposed in contact. It may have a hard gradation for the reproduction of line work or a soft gradation for the reproduction of continuous-tone originals.

One or more further layers may be provided, e.g. an adhesive layer between the emulsion layer and the imagereceiving layer as detailedly described above, a suitable subbing layer between the image-receiving layer and the support, a protective layer optionally having antistatic properties on top of the emulsion layer and one or more layers on the rearside of the material. An outer hydrophilic colloid layer on the rearside of the material may also contain finely divided pigment particles in order to improve the capability of this rearside to write on. The preferred concentration of these pigment particles falls Within the same limits mentioned above for the application of pigment particles in the image-receiving layer. Of course, the total concentration of pigment particles should not be choosen too high if it is intended to produce a transparent copy.

All kinds of ingredients may be present in at least one of the composing layer of the multilayer material, e.g., developing compounds, complexing agents for silver halide and compounds providing the boration as already referred to above. Further ingredients that may be present are preservatives for developing compounds, stabilizers, black-toning agents, anti-sludge agents, anti-yellowing agents, hardeners including latent hardeners, softening agents, latices and pigments.

Also the alkaline processing liquid may contain some further ingredients, e.g. developing compounds, preservatives for these developing compounds, a complexing agent for silver halide, a compound releasing bromide ions, calcium-sequestering compounds, black-toning agents, anti-sludge agents, harderers including latent hardeners, compounds providing the boration, anti-yellowing compounds etc.

The aqueous rinsing liquid for removing the silver halide emulsion layer may comprise some ingredients, e.g., weak acidifying agents, hardeners including latent hardeners, wetting agents, preservatives for developing compounds and anti-yellowing agents.

A photographic copy produced according to the present invention is especially suited for the preparation of a planographic printing plate according to the methods described and claimed in the Belgian patent specification 720,695 filed Sept. 12, 1968 by Gevaert-Agfa N.V., in the published Dutch patent applications 6800431 filed Jan. 11, 1968 and 6808599 filed June 19, 1968, both by Gevaert-Agft N.V., and in the "United Kingdom patent applications 60,837/ 68; 60,838/68 and 60,839/68 all filed Dec. 20, 1968 by Gevaert-Agfa N.V.

The following examples illustrate the present invention.

EXAMPLE 1 A suspension of the following composition was prepared:

water--950 ccs.

gelatin-30 g.

sodium alginate-10 g.

0.1% aqueous suspension of colloidal silver surphide-5 ccs.

20% aqueous solution of formaldehyde-2 ccs. sodium salt of oleyl methyl tauride--1 cc.

From this suspension an image-receiving layer was coated onto a paper support of g./sq.m. in such a way that the weight of the dried layer amounted to 2.5 g./ sq.m. To this image-receiving layer a second layer was applied, starting from the following solution:

hydroxyethyl-starch having a substitution degree of 0.27

of hydroxyethyl groups-10 g. water-4000 ccs.

50% solution of the sodium salt of dioctyl sulphosuccinic acid in water/ethanol (50/ 50)2 ccs.

This solution was coated in such a way that 1 1. covered 40 sq.m. of paper support.

After drying an orthochromatic and contrasty silver bromide emulsion containing per kg. 13 g. of silver bromide and 36 g. of gelatin was applied thereto in such a way that the finally obtained emulsion layer contained 2.4 g. of silver bromide per sq.m.

After image-wise exposure the thus prepared multilayer material was processed in an alkaline developing liquid of the following composition:

trisodium salt of ethylenediamine tetraacetic acid1.5 g. sodium sulphite75 g.

hydroquinone-20 g.

l-phenyl-3-pyrazolidinone1 g.

potassium bromide-2 g.

sodium thiosulphate-S g.

sodium hydroxide-12 g.

orthoboric acid2 g.

12.5 aqueous solution of saponine--5 ccs. polyethylene glycol (mol. weight:ca. 200)50 mg. water up to 1000 ccs.

The'silver halide emulsion layer strongly adhered to the image-receiving layer during this treatment.

Next, after the diffusion transfer image had been formed, the multilayer material was brought into rinsing water at room temperature and after some 20 to 30 seconds the silver halide emulsion layer detached as a coherent membrane without mechanical help. In the imagereceiving layer a positive diifusion transfer image of the original was obtained.

EXAMPLE 2 The method of Example 1 was repeated, however, after the orthoboric acid had been omitted from the alkaline processing liquid and had been added to the coating solution of the hydroxethyl starch layer in an amount of g. per litre of this solution.

By proceeding in this manner an excellent adhesion of the emulsion layer to the image-receiving layer during the treatment with the alkaline developer was obtained.

At the subsequent treatment of the multilayer material in rinsing water the emulsion layer detached after some 30 seconds without mechanical help. A diffusion transfer copy of good quality was obtained.

EXAMPLE 3 The method of Example 1 was repeated, however, after the orthoboric acid of the alkaline processing liquid has been replaced by 3 g. of borax per litre of said liquid.

Besides, the binder of the light-sensitive silver bromide emulsion layer consisted of gelatin and the same type of hydroxyethyl starch used in the preparationof the layer between the image-receiving layer and the silver halide emulsion layer, the gelatin in an amount of 1.8 g. and the hydroxyethyl starch in an amount of 0.5 g. per sq.m. of the multilayer material.

During processing in the alkaline developing liquid the silver halide emulsion layer strongly adhered to the imagereceiving layer.

However, at the subsequent rinsing stage in water the silver halide emulsion layer detached in some 45 seconds in the form of very small flakes. A positive diffusion transfer copy of good quality was obtained.

EXAMPLE 4 The method of Example 1 was repeated, however, after the orthorboric acid had been omitted from the alkaline processing liquid and borax had been added to the coating composition of the image-receiving layer in an amount of g. per litre of this composition.

Besides, the binder of the light-sensitive silver bromide emulsion layer consisted of gelatin and a copolymer comprising 88 mole percent of vinyl alcohol and 12 mole percent of vinyl acetate units, the viscosity of a 4% aqueous solution at 20 C. amounts to 35-45 cps. in an amount of 1.8 g. and 0.5 g. respectively per sq.m. of the multilayer material.

During development of the multilayer material in the alkaline developing liquid and the subsequent treatment in rinsing water, the multilayer material behaved about as described in Example 3. A diffusion transfer copy of a good quality was obtained.

EXAMPLE 5 The method of Example 1 was repeated, however, after the orthoboric acid had been omitted from the alkaline processing liquid and borax had been added to the coating solution of the hydroxyethyl starch layer in an amount of 15 g. per liter of this solution.

Besides, the binder of the light-sensitive silver bromide emulsion layer consisted of gelatin and gum arabic in an amount of 1.8 g. and 1.9 g. respectively per sq.m. of the multilayer material.

During the development of the multilayer material in the alkaline developing liquid and the subsequent treatment in rinsing water, the multilayer material behaved about as described in Example 3. A diffusion transfer copy of a good quality was obtained.

EXAMPLE 6 The method of Example 1 was repeated, however, after the layer of hydroxyethyl starch between the image-receiving layer and the silver halide emulsion layer as well as the orthoboric acid of the alkaline processing liquid had been omitted.

Besides, the binder of the light-sensitive silver bromide emulsion layer consisted of gelatin and gum arabic, in an amount of 1.8 g. and 1.9 g. respectively per sq.m. of the multilayer material. In addition thereto 20 g. of boric acid had been added per kg. of light-sensitive coating com position.

During the development of the multilayer material in the alkaline developing liquid and the subsequent treatment in rinsing water, the multilayer material behaved about as described in Example 3. A diffusion transfer copy of a good quality was obtained.

EXAMPLE 7 The method of Example 1 was repeated, however, after the 1-phenyl-3pyrazolidinone developing compound present in the aqueous alkaline developing liquid had been replaced by 1.2 g. of 1-phenyl-4-methyl-3-pyrazolidinone. About the same results were obtained.

EXAMPLE 8 The method of Example 1 was repeated, however, after the aqueous alkaline developing liquid had been replaced by the following alkaline processing liquid that was free from developing substances:

trisodium salt of ethylenediamine tetraacetic acid1 g. sodium sulphite40 g.

potassium bromide-1 g.

sodium thiosulphate3 g.

trisodium phosphate-12-water-6O g.

orthoboric acid-2 g.

12.5% aqueous solution of saponine-5 ccs.

sodium salt of dioctylsulfosuccinic acid mg. water up to 1000 ccs.

To the light-sensitive silver bromide coating composition 1-phenyl-3-pyrazolidinone and hydroquinone were added in such an amount that per sq.m. of the multilayer material 0.1 g. of 1-phenyl-3-pyrazolidinone and 1.5 g. of hydroquinone were present.

About the same results were obtained, but the alkaline processing liquid possessed better keeping qualities.

9 EXAMPLE 9 Water 800 COS.

Gelatin 37 g. 0.1% aqueous dispersion of colloidal silver sulphide 12 cos. aqueous solution of the addition product of sodium hydrogen sulfite to 2,4-toluene diisocyanate according to the formula:

50 cos.

H3O N HCO-SOsNa NHCO-SOaNa 12% aqueous solution of saponine. 15 cos. 20% aqueous dispersion of barium sulphate 125 ccs. 20% aqueous solution of formaldehyde P 10 ccs.

To the dry image-receiving layer an intermediate layer was coated by applying the following solution at a rate of 28 cos. per sq.m.:

hydroxyethyl-starch having a substitution degree of 0.27

of hydroxyethyl groups10 g.

water-950 ccs.

12% aqueous solution of saponine-40 ccs.

On top of the dry intermediate layer an orthochromatic high-sensitive and high contrast gelatin silver bromide emulsion layer was applied. Per sq.m. 7.3 g. of gelatin and 6.5 g. of silver bromide are present.

The multilayer material thus obtained was imagewise exposed in a camera and then processed for some 2 minutes in an alkaline developing liquid as described in Example 1, this liquid, however, containing 15 g. of sodium thiosulphate instead of 5 g.

The silver halide emulsion layer strongly adhered to the image-receiving layer during this treatment.

Next, after the diffusion transfer image had formed, the multilayer material was brought into rinsing water at room temperature and after some to 30 seconds the silver halide emulsion layer detached as a coherent membrane without mechanical aid. A positive transparency of the original was obtained.

We claim:

1. Method of copying according to the silver complex diflFusion transfer process using a multilayer material comprising in order a support, an image-receiving layer and a light-sensitive silver halide emulsion layer, said emulsion layer having incorporated therein as its essential binding agent a macro-molecular carbohydrate having a plurality of pairs of cis-hydroxy groups thereon and capable of forming with borate anions a pH reversible gel which is insoluble in an alkaline solution and substantially soluble in a non-alkaline solution, which comprises the steps of treating said multilayer material after imagcwise exposure thereof with an aqueous alkaline processing liquid in the presence of a photographic developing agent for silver halide, a complexing agent for silver halide and a compound releasing orthoborate anions, and thereafter washing said material with a non-alkaline aqueous rinsing liquid, whereby said emulsion layer is readily removed without substantial mechanical assistance.

2. Method according to claim 1, wherein the macro molecular compound having cis-hydroxy groups is a filmforming binding agent and constitutes from 10 to 70% of the total weight of the binder of said light-sensitive silver halide emulsion layer.

3. Method according to claim 1, wherein the macromolecular compound having cis-hydroxy groups consists essentially of at least one member of the group consisting of partially saponified polyvinyl acetate, polyvinyl alcohol, gum arabic, and an hydroxyalkyl starch.

4. Method according to claim 2, wherein the macromolecular compound having cis-hydroxy groups comprises or consists of hydroxyethyl starch.

5. Method according to claim 2, wherein the macromolecular compound having cis-hydroxy groups comprises or consists of hydroxypropyl starch.

6. Method according to claim 1 wherein the orthoborate anions are provided by a compound dissolved in the aqueous alkaline processing liquid.

7. Photographic multilayer copying material for use in the silver complex diffusion transfer process, said material comprising in order a support, an image-receiving layer and a light-sensitive silver halide emulsion layer, said emulsion layer having incorporated therein as the essential binding agent thereof a macro-molecular carbohydrate compound having a plurality of pairs of cis-hydroxy groups and capable of forming with borate anions a pH reversible gel which is insoluble in an alkaline solution and substantially soluble in a non-alkaline solution, said material having at least one layer containing a compound providing orthoborate anions in water-permeable contact with said emulsion layer.

8. Photographic multilayer material according to claim 7, wherein the macromolecular compound having cishydroxy groups is a film-forming binding agent and constitutes from 10 to 70% of the total weight of the binder of said light-sensitive silver halide emulsion layer.

9. Photographic multilayer material according to claim 7, wherein the macromolecular compound having cishydroxy groups comprises or consists of at least one member of the group consisting of partially saponified polyvinyl acetate, polyvinyl alcohol, gum arabic and an bydroxyalkyl starch.

10. Photographic multilayer material according to claim 7, wherein the compound providing orthoborate anions is present in the multilayer material in an amount between about mg. and 50 g. per sq. m.

11. Method of copying according to the silver complex diifusion transfer process using a multilayer material comprising in order a support, an image-receiving and a lightsensitive silver halide emulsion layer, and a supplemental layer intermediate the emulsion layer and the image-receiving layer, said supplemental layer having incorporated therein as the essential binding agent thereof a macromolecular carbohydrate having a plurality of pairs of cis-hydroxy groups thereon and capable of forming with borate anions a pH reversible gel which is insoluble in an alkaline solution and substantially soluble in a nonalkaline solution, which comprises the steps of treating said multilayer material after imagewise exposure thereof with an aqueous alkaline processing liquid in the presence of a photographic developing agent for silver halide, a complexing agent for silver halide: and a compound releasing orthoborate anion, and thereafter washing said material with a non-alkaline aqueous rinsing liquid, whereby said emulsion layer is readily removed without substantial mechanical assistance.

12. Method according to claim 11 wherein the macromolecular compound having cis-hydroxy groups is a filmforming binding agent and constitutes from 20 to 100% of the total Weight of the binder of said supplemental layer.

13. Method according to claim 11 wherein the macromolecular compound having cis-hydroxy groups consists essentially of at least one member of the group consisting of partially saponified polyvinyl acetate, polyvinyl alcohol, gum arabic, and an hydroxyalkyl starch.

14. Method according to claim 12 wherein the macromolecular compound having cis-hydroxy groups is bydroxyethyl starch.

15. Method according to claim 12 wherein the macromolecular compound having cis-hydroxy groups is hydroxypropyl starch.

16. Method according to claim 11 wherein the orthoborate anions are provided by a compound dissolved in the aqueous alkaline processing liquid.

17. Photographic multilayer copying material for use in the silver complex diffusion transfer process, said material comprising in order a support, an image-receiving layer and a light-sensitive silver halide emulsion layer, and a supplemental layer intermediate said emulsion layer and said image receiving layer, said supplemental layer having incorporated therein as the essential binding agent thereof a macromolecular carbohydrate compound having a plurality of pairs of cis-hydroxy groups and capable of forming with borate anions a pH reversible gel which is insoluble in an alkaline solution and substantially soluble in a non-alkaline solution, said material having at least one layer containing a compound providing orthoborate anions in Water-permeable contact with said supplemental layer.

18. Photographic multilayer material according to claim 17, wherein the macromolecular compound having cis-hydroxy groups is a film-forming binding agent and constitutes from 20 to 100% of the total weight of the binder of said supplemental layer.

19. Photographic multilayer material according to References Cited UNITED STATES PATENTS 2,558,857 7/1951 Land 96- 29 917,310 4/1909 Kelly et a1 96-76 2,543,181 2/1951 Land 96-29 OTHER REFERENCES Crawley: Brit J Phot, 113, #5542, pp. 892-893.

20 NORMAN G. TORCHIN, Primary Examiner J. L. GOODROW, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,684,508 Dated August 15, 1972 lnventofls) Emiel Alexander HOFMAN et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the Patent, insert Assignee: Agfa-Gevaert Morts-el, Belgium Signed and sealed this 8th day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer I Commissioner of Patents 'ORM PO-1050 (10-69) USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE: I989 0-366-334 

